Optical disk vibration sensing and reproducing device

ABSTRACT

In an optical disk reproducing device capable of rotating an optical disk at a selected one of a plurality of preset linear velocities, vibration or shock of the device is detected during rotation of the disk, and the linear velocity of the disk is determined based on the result of the detection of the vibration or shock to restrain the vibration and shock within a permissible range. A limit rotational velocity above which the vibration or shock is excessive may be determined during a test conducted each time a disk is inserted, and the linear velocity of the disk during reproduction may be determined such that the rotational velocity does not exceed the limit rotational velocity.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 08/855,252filed May 13, 1997 entitled: "OPTICAL DISK VIBRATION SENSING ANDREPRODUCING DEVICE". U.S. Pat. No. 5,886,966.

BACKGROUND OF THE INVENTION

The present invention relates to an optical disk reproducing device, andin particular an optical disk reproducing device which is capable ofchanging the linear velocity in accordance with the vibration of thedevice.

The linear velocity at which commercially available optical diskreproducing devices can operate is increasing year by year. In the caseof CD-ROM drives for use with personal computers, the velocity isincreasing from x1, to x2, x4, x6, and so on, and many of the CD-ROMdrives are designed to operate at a selected one of a plurality oflinear velocities.

The rotational velocity of the disk increases with the linear velocity.While the rotational velocity at the inner radial part is about 500 rpmwith the standard velocity (x1 velocity), it is as high as 3000 rpm withthe x6 velocity. With the increase in the velocity, vibrations increaseand may become problematical. The increased vibrations may affect ordisable the signal reading. The vibrations are caused by various factorssuch as eccentricity of the disk, variation in the position at which thedisk is held, and unevenness in thickness of the disk. For instance, acommercially available CD-ROM disk with a nominal thickness of 1.2 mmhas a thickness difference of 0.1 mm between the maximum and minimumthicknesses.

SUMMARY OF THE INVENTION

Accordingly, an object of the invention is to provide an optical diskreproducing device capable of operating at a maximum velocity while atthe same time avoiding failure of reading.

According to the invention, there is provided an optical diskreproducing device comprising:

means for rotating an optical disk at a selected one of a plurality oflinear velocities;

means for reading data from the disk while the disk is rotated;

means for detecting vibration or shock of the device during rotation ofthe disk; and

a velocity control circuit for determining the linear velocity of thedisk based on the result of the detection of the vibration or shock.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a block diagram showing a pertinent part of the CD-ROM diskreproducing device of an embodiment of the invention; and

FIG. 2 and FIG. 3 are flowcharts showing the control operation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the invention will now be described withreference to the drawings. FIG. 1 shows an embodiment of the invention.

The CD-ROM drive of this embodiment comprises a spindle motor 2 forrotating a CD-ROM disk 1. The CD-ROM disk 1 stores data representingcharacters, sound, images and the like along spiral tracks. At theinnermost radial part of the disk is a TOC (table of contents) area,where addresses and the like of the respective pieces of data arestored. The above-mentioned data representing characters, sound, imagesand the like is stored in the data area which is outside of the TOCarea.

An objective lens 4 converges the laser beam from a laser diode which isnot shown, to form a beam spot on the surface of the disk, at which thedata is read from the disk. The objective lens 4 also receives anddirects the light reflected from the surface of the disk 1 to afocus/tracking controller 11.

A focusing unit 5 includes a focusing coil 6 and a focusing magnet 7.The lens 4 is supported by a lens support 4s. The focusing coil 6 issupported by the lens support 4s, and is thereby effectively fixed tothe lens 4. The focusing magnet 7 is held by a pick-up frameschematically indicated by dotted line PU. The focusing coil 6 and thefocusing magnet 7 cooperate to cause movement of the objective lens 4toward and away from the disk surface, i.e., in the focusing direction,in response to a focusing control signal supplied from thefocus/tracking controller 11.

A tracking unit 11 includes a tracking coil 9 and a tracking magnet 10.The tracking coil 9 is supported by the lens support 4s, and is therebyeffectively fixed to the lens 4. The tracking magnet 10 is held by thepick-up frame PU. The lens support 4s is also supported by the pick-upframe PU such that the tracking coil 9 and the tracking magnet 10cooperate to cause movement in the radial direction of the disk, i.e.,in the tracking direction, in response to a tracking control signalsupplied from the focus/tracking controller 11.

The focus/tracking controller 11 detects a focusing error and a trackingerror based on the light reflected from the disk, and supplies thefocusing control signal to the focusing unit 5 and the tracking controlsignal to the tracking unit 8. The focusing/tracking controller 11 alsooutputs a reproduced signal RS from the disk 1.

A motor controller 3 controls the rotational velocity of the spindlemotor 2 in synchronism with the clock contained in the reproduced signalRS from the disk 1, supplied from the focus/tracking controller 11. Thecontrol over the rotation is for CLV (constant linear velocity), whereinthe rotational velocity is lowered as the beam spot from the objectivelens 4 moves radially outward on the disk (for scanning along thetracks) to maintain the linear velocity constant. The device is capableof operating in a selected one of a plurality of velocity modes, forrespective velocities, namely, x1, x2, x4, x6 and x8 velocities, wherex1 represents the standard velocity, and x2, x4, x6 and x8 respectivelyrepresent the twice, four times, six times and eight times the standardvelocity. The rotational velocity varies over the following ranges forthe respective velocity mode.

    ______________________________________                                                   ×1 530 to 200 rpm                                                       ×2 1060 to 400 rpm                                                      ×4 2120 to 800 rpm                                                      ×6 3180 to 1200 rpm                                                     ×8 4240 to 1600 rpm                                          ______________________________________                                    

A feature of the embodiment is that the vibration and shock (representedby acceleration) are detected, and a limit rotational velocity abovewhich the vibration or shock is excessive is determined, in a test modeof operation which is conducted immediately after and each time a diskis inserted.

In the reproduction mode of operation in which the data in the disk isreproduced, which is conducted after the test mode of operation, thelinear velocity is controlled such that the rotational velocity does notexceed the limit rotational velocity. The linear velocity which can beselected is one of the discrete values (x1, x2, x4, . . . ), and thecontrol is such that the linear velocity is switched to a higher valueas the beam spot moves radially outwards and reaches a position at whichthe switching to the higher linear velocity does not cause therotational velocity to exceed the limit rotational velocity.

To determine the limit rotational velocity above which the vibration orshock becomes excessive, an arrangement for detecting vibration andshock is provided.

In the embodiment under consideration, the vibration and shock aredetected when the beam spot is at the innermost radial part, and thedisk is rotated in each of the various linear velocities. If thevibration and shock for one linear velocity are not excessive, and thevibration or shock for the linear velocity higher by one step isexcessive, the rotational velocity corresponding to said one linearvelocity (with the beam spot being at the innermost radial part) isfound to be the limit rotational velocity.

If the vibration and shock for the highest linear velocity (x8) are notexcessive, then the rotational velocity corresponding to said highestlinear velocity (with the beam spot being at the innermost radial part)is found to be the limit rotational velocity.

What follows is the description of the arrangement for detecting thevibration and shock.

An electromotive force is induced in the focusing coil 6, due todisplacement between the focusing coil 6 and the focusing magnet 7, dueto vibration. In this embodiment, this electromotive force is utilizedfor detecting the vibration.

Similarly, an electromotive force is induced in the tracking coil 9, dueto displacement between the tracking coil 9 and the tracking magnet 10,due to vibration, and in this embodiment, this electromotive force isalso utilized for detecting the vibration.

A shock sensor 17 is fixed to the pick-up frame PU, to detect anacceleration of the pick-up frame PU.

A system controller 13 comprises a microprocessor, and controls thevarious parts of the drive device in accordance with the programs storedin a ROM 14. Specifically, the system controller 13 specifies the linearvelocity for the disk 1 based on the electromotive force generated inthe focusing unit 5, and amplified by a focusing amplifier 15, theelectromotive force generated in the tracking unit 8, and amplified by atracking amplifier 16, and a detection signal from the shock sensor 12.

A RAM 17 stores data required for the operation of the system controller13, such as data indicating the threshold value for the electromotiveforces representing vibrations and acceleration representing shock abovewhich the vibration or shock is found to be excessive, and the limitrotational velocity which should not be exceeded for preventing thevibration and shock from exceeding their threshold values.

A focusing switch 18 is controlled by the system controller 13 toselectively connect the focusing unit 5 with the focusing/trackingcontroller 11 to enable focusing control, or to the system controller 13via the focusing amplifier 15 to enable detection of vibration.

A tracking switch 19 is controlled by the system controller 13 toselectively connect the tracking unit 8 with the focusing/trackingcontroller 11 to enable tracking control, or to the system controller 13via the tracking amplifier 16 to enable detection of vibration.

FIG. 2 shows the operation of the system controller 13 performedaccording to the program stored in the ROM 14.

When it is detected that a disk 1 is inserted into the reproducingdevice (S1), the focusing switch 18 and the tracking switch 19 areturned to contacts 18a and 19a to connect the focus/tracking controller11 to enable focus control and tracking control (S2).

The linear velocity is made to be the standard velocity, and the data inthe TOC area is read (S3, S4). The data in the TOC area is important asinitial data. Accordingly that the velocity is set to be the standardvelocity, rather than x8 velocity.

Then, the focusing switch 18 is turned to contact 18b to connect to thefocusing amplifier 15, and the tracking switch 19 is turned to contact19b to connect to the tracking amplifier 16 (S5). The beam spot ismaintained at the innermost radial part of the disk. The systemcontroller 13 directs the motor controller 3 to increase the linearvelocity of the disk 1 to the x8 velocity (S6). No control signals aretherefore supplied to the focusing coil 6 and the tracking coil 9, andthe electromotive forces due to vibration are supplied through thefocusing amplifier 15 and the tracking amplifier 16 to the systemcontroller 13, and information on the acceleration is also supplied fromthe shock sensor 12 to the system controller 13 (S7).

As was described, stored in the RAM 17 are threshold values for theelectromotive force from the focusing amplifier 15, the electromotiveforce from the tracking amplifier 16, and the output from the shocksensor 12. If any of the threshold values are exceeded, it is judgedthat the threshold for vibration or shock is found to be exceeded (S8).Then, it is checked whether the disk linear velocity is at the standardvelocity (x1), at step S9. If the disk is at the standard velocity, nofurther reduction is possible. The vibration or shock is excessive evenat the standard velocity (S11), and the operation ends. If at the stepS9, the velocity is not at the standard the velocity, then velocity islowered (S10) by one step, e.g., from the x8 to x6, in other words, to avelocity one step lower than the velocity before the change. By thevelocity reduction, vibration and shock are reduced.

After the velocity is reduced, then the vibration and the shock areagain tested. If the vibration or shock still exceeds the thresholdvalue, the velocity is again lowered by another step, from the x6 to x4velocity. The velocity reduction is repeated step by step, from x4 tox2, and x2 to x1 (S7 to S10), until the vibration and shock are found tobe smaller than the threshold values (S7 to S10).

When the vibration and shock are found non-excessive for the first timein the above sequence of operations. (Yes at S8), the rotationalvelocity at which the disk is rotated when the linear velocity is set,and the beam spot is at the innermost radial part is determined as thelimit rotational velocity, and stored in the RAM 17 (S12).

At step S12, the radial position of the disk at which the linearvelocity can be switched to a higher value by one step without causingthe rotational velocity to exceed the limit rotational value isdetermined, and the address of the track or sector at the radialposition is stored in the RAM 17.

For instance, if it has been found that the linear velocity which doesnot cause excessive vibration and shock while the beam spot is at theinnermost radial part is x1, then the limit rotational velocity is 530rpm. The radial position at which the rotational velocity is reduced tothis limit rotational velocity is determined for other linearvelocities. In this case, such a position can exist only for the linearvelocity x2. The address of the track or sector at this radial positionis then determined and stored in the RAM 17.

After the step S12, the focusing switch 18 and the tracking switch 19are turned back to the contacts 18a and 19a, to connect thefocus/tracking controller 11, to enable the focusing control andtracking control (S13).

The preceding discussion describes how the vibration and shock aredetected each time the disk is inserted. During reproduction of datafrom the disk, the linear velocity is so controlled that the rotationalvelocity does not exceed the. limit value.

FIG. 3 is a flowchart showing the operation of the controller accordingto the program stored in the ROM 14, which is performed while the dataon the disk is being reproduced, after the limit rotational velocity isset.

As was described above, the disk 1 is rotated with a constant linearvelocity, so that the rotational velocity is gradually lowered as thebeam spot moves radially outwards. For instance, the range of thevariation of the rotational velocity for each of the standard and doublevelocities is as follows:

standard velocity (x1): 530 to 200 rpm

double velocity (x2): 1060 to 400 rpm

The maximum rotational velocity for the standard velocity is higher thanthe minimum rotational velocity for the double velocity, and thereforewhen the beam spot is radially more inward than a certain position (atwhich the rotational velocity is 530 rpm if the linear velocity is x2),the rotational velocity is below the maximum rotational velocity for thestandard linear velocity. This is also true between the x4 velocity andthe x2 velocity, between the x6 velocity and the x4 velocity, andbetween the x8 velocity and the x6 velocity.

The motor controller 3 has a capturing range of ±50%. If the rotationalvelocity is doubled, from 250 rpm to 500 rpm, for example, by transitionfrom the standard linear velocity mode to the double linear velocitymode, the velocity before the switching is -50% with respect to thevelocity after the switching, so that it is within the capturing range,and the data can be read without interruption.

As was mentioned, the address of the track or a sector at the positionat which the linear velocity may be switched to a higher value withoutcausing the rotational velocity to exceed the limit rotational velocityis stored in the RAM 17 for each linear velocity. During reproduction ofdata from the disk, when the beam spot reaches such a position, thelinear velocity is increased by one step (S21 to S29), and the readingis continued. This enables the increase in the average velocity of thedata reading, and also ensures correct data reading.

In the embodiment described, the focusing unit 5, the tracking unit 8,and the shock sensors 12 are used. It is not necessary to use all ofthese three. For instance, only one of them may be provided. However, ifthe vibration is detected based only on the electromotive force from thefocusing unit 5 or the electromotive force from the tracking unit 8, thedetection could be effected using different sensitivities andcharacteristics between the vibration in the direction normal to thesurface of the disk and the vibration in the radial direction of thedisk.

Detection of the vibration may be achieved by using other parts whichfor example already form part of the device.

In the embodiment described, the TOC area is scanned with the standardvelocity, irrespective of the velocity for reading the data area. Thishowever does not impose a limitation: the TOC area may also be scannedwith the same velocity as the data area.

In the embodiment described, the limit rotational velocity is determinedas the rotational velocity at which the disk is rotated when the beamspot is at the innermost radial part, and when the vibration and shockare found non-excessive for the first time while the linear velocity isdecreased step by step.

The margin by which the vibration and shock are below their thresholdvalues at the time when the vibration and shock are found to benon-excessive for the first time may be taken into consideration whendetermining the limit rotational velocity. For instance, if thevibration or shock (which is closer to its threshold) is found to beless than its threshold by a certain percentage M (e.g., M=20%) when thelinear velocity is x1and the beam spot is at the innermost radial part(so that the rotational velocity is 530 rpm), the limit rotationalvelocity is determined to be

    530/(1-M/100)=530/0.8=662.5 rpm

In this case, the position at which the switching of the linear velocityto a higher value takes place is set to be the position at which therotational velocity after the switching is 662.5 rpm.

In the example under consideration, the limit rotational velocity is setat the rotational velocity (e.g., 530 rpm) at which the disk is rotatedwhen the beam spot is at the innermost radial part of the disk and thevibration and shock are found to be non-excessive for the first time. Asan alternative or in addition, the rotational velocity (e.g., 500 rpm) alittle smaller than the above-mentioned rotational velocity (530 rpm)may be stored (the secondary limit rotational velocity), and is used forthe purpose of switching to a different linear velocity. This is to givean operational margin. For distinction from the "secondary limitrotational velocity", the limit velocity for the linear velocity x1,which is 530 rpm, is called a "primary limit rotational velocity".

That is, the system controller 13 permits the rotation at 530 rpm onlyat the linear velocity x1, and restricts the rotational velocity to 500rpm at other linear velocities.

In the embodiment described, the beam spot is fixed at the innermostradial part of the disk, and the linear velocity is switched step bystep, and the rotational velocity velocity is switched between discretevalues. As an alternative, the rotational velocity may be changedcontinuously, or substantially continuously (independent of therotational velocities at which the disk is rotated when the beam spot isat the innermost radial part and the linear velocity is at therespective discrete values x1, x2, x4, . . . ), and the maximum velocityat which the vibration and the shock do not exceed their thresholdvalues found, and determined to be the limit rotational velocity.

To find such a maximum velocity, the rotational velocity may begradually decreased from the highest velocity for the highest linearvelocity, and the rotational velocity at which the vibration and shockare both found non-excessive for the first time may be determined as themaximum velocity and hence the limit rotational velocity. Alternatively,a binary search method may be used to find such a maximum velocity.

To find the maximum velocity through gradual decrease, the operationsimilar to that shown in FIG. 2 may be performed. However, at the stepS10, where the linear velocity is lowered by one step (S10), therotational velocity should be lowered by a certain unit amount.

In the embodiment described, the maximum linear velocity is x8. Thishowever does not impose a limitation. The invention is applicable to anoptical disk reproducing device capable of operating an even higherlinear velocity.

What is claimed is:
 1. An optical disk reproducing devicecomprising:means of rotating an optical disk at a selected one of aplurality of linear velocities; means for reading data from the diskwhile the disk is rotated; means for detecting vibration or shock of thedevice during rotation of the disk; a velocity control circuit forsetting the linear velocity of the disk to be one of the plurality oflinear velocities based on the result of the detection of the vibrationor shock; wherein said velocity control circuit sets the linear velocityof the disk such that the rotational velocity does not exceed arotational velocity limit.
 2. The device according to claim 1, whereinsaid velocity control circuit causes the linear velocity to be one ofthe plurality of linear velocities; andwhile a beam spot for readingdata from the disk is moving radially outwards, said velocity controlcircuit switches the linear velocity to a higher one of the linearvelocities at a point where such switching does not result in therotational velocity exceeding said rotational velocity limit.
 3. Thedevice according to claim 1, wherein said velocity control circuitdetects the linear velocity at which the vibration or shock is excessivewhen the beam spot is at the innermost radial part of the disk, andfinds a corresponding rotational velocity as a rotational velocitylimit.
 4. The device according to claim 1, wherein said velocity controlcircuit causes the rotational velocity to decrease gradually, and findsthe rotational velocity at which the vibration or shock is not excessivefor the first time as said rotational velocity limit.
 5. The deviceaccording to claim 1, wherein said velocity control circuit performs thedetermination of said rotational velocity limit each time a disk isinserted.
 6. The device according to claim 1, wherein said deviceselectively operates in a test mode and in a reproduction mode, saidvelocity control circuit performing the determination of the rotationalvelocity limit in said test mode, and performing the control over thelinear velocity in the reproduction mode so that the rotational velocitydoes not exceed the rotational velocity limit.
 7. The device accordingto claim 6, wherein when the rotational velocity limit is determined insaid test mode, said velocity control circuit causes a memory to storean address of a track or a sector at a point where the linear velocityshould be switched to a higher value while the beam spot is movingradially outwards, said point being at a position where such switchingdoes not result in the rotational velocity exceeding said rotationalvelocity limit, andwhen the beam spot reaches said point in thereproduction mode said velocity control circuit causes the switching ofthe linear velocity.
 8. The device according to claim 1, furthercomprising:a lens for converging the laser beam illuminating the disk;and tracking means for detecting a tracking error and moving the lens inthe radial direction of the disk; wherein said detecting means detectsthe vibration responsive to operation of the tracking means.
 9. Thedevice according to claim 8, wherein said tracking means detects thetracking error based on light reflected from the disk.
 10. The deviceaccording to claim 8, wherein said detecting means detects the vibrationbased on the electromotive force generated in the tracking means.
 11. Anoptical disk reproducing device comprising:means for rotating an opticaldisk at a selected one of a plurality of linear velocities; means forreading data from the disk while the disk is rotated; means fordetecting vibration or shock of the device during rotation of the disk;a velocity control circuit for setting the linear velocity of the diskto be one of the plurality of linear velocities based on the result ofthe detection of the vibration or shock; a lens for converging the laserbeam illuminating the disk; and tracking means for detecting a trackingerror and moving the lens in the radial direction of the disk; whereinsaid detecting means detects the vibration responsive to operation atthe tracking means.
 12. The device according to claim 11, wherein saidtracking means detects the tracking error based on light reflected fromthe disk.
 13. The device according to claim 11, wherein said detectingmeans detects the vibration based on the electromotive force generatedin the tracking means.